The title compound, [Yb(C5HF6O2)2(C20H14N4)(H2O)]Cl·CH3OH·H2O, adopts an eight-coordinated geometry around the YbIII atom consisting of a 4'-(4-pyridyl)-2,2':6',2''-terpyridine (pytpy) ligand, two 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac) anions and an aqua ligand. In the solid state, the compound forms supramolecular chains running along the b-axis via intermolecular hydrogen bonds between the Yb-OH2 unit and the N-atom donor of the 4-pyridyl pendant of pytpy, with an ON distance of 2.686 (4) Å. A chloride counter-anion and lattice methanol and water solvent molecules occupy a hydrophilic columnar space along the coordination chains. O-HCl hydrogen bonds occur. The two water molecules and the four trifluoromethyl groups are disordered over two sets of sites, each with different occupancy ratios.

The molecular design of multidentate ligands is crucial to determining
structures and functions of the resulting coordination compounds and
metallo-supramolecular systems. Specifically, a tetradentate ligand
4'-(4-pyridyl)-2,2':6',2"-terpyridine (pytpy) provides a unique structural
feature as a bridging ligand where two different coordination donors, the
tridentate terpyridyl and monodentate pyridyl moieties, are both associated
with metal coordination. Herein we report an unusual bridging mode of pytpy in
a one-dimensional metallo-supramolecular system as exemplified with an X-ray
crystal structure of compound (I), where the monodentate pyridyl arm in pytpy
is now bound to the neighboring molecule via intermolecular hydrogen
bonding to form a one-dimensional supramolecular chain. Compound (I) consists
of a monocationic complex [YbIII(pytpy)(hfac)2(H2O)], a Cl- anion, and
lattice solvents, CH3OH and H2O. The YbIII center is surrounded by three
N donors from pytpy and five O donors from two hfac chelates and one aqua
ligand completing the 8-coordinate geometry as shown in Figure 1. Among
structurally determined YbIII complexes containing a single terpyridine
ligand, the coordination number 8 is rather unusual and 9- and 10-coordination
is more commonly observed (Hayashi et al., 1998; Ahrens et
al., 2002; Fukuda et al., 2002; Przychodzen et
al., 2007; Li
et al., 2007; Xu et al., 2009; Stojanovic et
al., 2010).
The 8-coordination around lanthanide(III) ions are seen, for example, in
[LnIII(Trop)4]- [Trop = tropolonene
(2-hydroxycyclohepta-2,4,6-trienone)] (Zhang et al.,
2007a). In
compound (I), the Yb—N(pytpy) lengths vary from 2.434 (3) to 2.464 (3) Å
and the Yb—O(hfac) lengths from 2.262 (3) to 2.334 (3) Å; these values
compare well with those observed in complexes containing the
[YbIII(tpy)(hfac)3] entity (Li et al., 2007; Xu et
al.,
2009). There is a hydrogen-bonding interaction with the chloride anion
with an
O5···Cl1i (symmetry code: (i) 1 + x, y, z) distance
of 3.054 (3) Å and an O6···Cl1 distance of 3.102 (3) Å. An additional
hydrogen-bonding interaction is seen between the N atom of the dangling
pyridyl group and the aqua ligand in the neighboring molecule with an
O5···N4ii (symmetry code: (ii) x, 1 + y, z)
distance of 2.686 (4) Å to form one-dimensional supramolecular chains
of [Yb(pytpy)(hfac)2(H2O)]+ units running along the b-axis.
Similar hydrogen bonded one-dimensional networks including pytpy moieties
have been also reported (Beves et al., 2007b;
Beves et al., 2008).

H atoms except those of water were placed in geometrically idealized
positions and constrained to ride on their parent atoms with
Uiso(H) = 1.2Ueq(C—H) or 1.5Ueq(O—H).

The lattice water shows positional disorder which is modeled as two oxygen
atoms, O7A and O7B, with site occupancies of 0.58 and 0.42, respectively.
The O7A—O7Aiii (symmetry codes: (iii) 1 - x, 2 - y, 1 -
z) distance was restrained to 2.56 (1) Å using the DFIX
command of the program SHELXTL (Sheldrick, 2008) because of a
strong correlation between positional parameters of the two components
of the disorder.

H atoms attached to O5 (H5A and H5B) and lattice water (H7A, H7B, H7C, and H7D)
were found in a difference Fourier map. The O—H and H—H distances within
the water molecules were restrained to 0.83 (7) Å)
and 1.35 (8) Å , respectively, by using the
DFIX command for a stable refinement. Hydrogen atoms on the lattice
water were not included in the structure factor calculation.

Four trifluoromethyl groups were found to show disorder. The geometries of the
trifluoromethyl groups were constrained by using the SAME command. Anisotropic
displacement parameters of the pairs of overlapping disordered atoms of the
major and minor components of the disorder were made equal using the EADP
constraints. The final occupancies of the disordered CF3 groups were found
to be 0.81:0.19, 0.76:0.24, 0.90:0.10, and 0.86:0.14 for (C21A, F1A, F2A,
F3A)/(C21B, F1B, F2B, F3B), (C25A, F4A, F5A, F6A)/(C25B, F4B, F5B, F6B),
(C26A, F7A, F8A, F9A)/(C26B, F7B, F8B, F9B), and (C30A, F10A, F11A,
F12A)/(C30B, F10B, F11B, F12B), respectively.

Fig. 1. An ORTEP view of the title compound, with the atom-labelling scheme.
Displacement ellipsoids are drawn at the 50% probability level. The minor
component of the disordered CF3 groups and lattice water are omitted for
clarity.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.

This work was supported by a Grant-in-Aid for Scientific Research on Innovative
Areas "Coordination Programming" (No. 22108523) and "Molecular Activation"
(No. 23105537), Grant-in-Aid for Scientific Research (A) (No. 21245016) and
(B) (No. 20350029), and the Global COE Program "Science20 H14 for Future
Molecular Systems" from the Ministry of Education, Culture, Sports, Science
and Technology of Japan. MA also acknowledges financial support by the
Tokuyama Science Foundation.